1. Protein kinase C is considered to be ubiquitous in tissues and organs; however, its isolation and characterization have been principally with adult mammalian tissues. 2. There is increasing evidence for the importance of this enzyme during early development. 3. In this study, protein kinase C has been identified and partially characterized in cytosolic fraction from sea urchin eggs. 4. The enzyme was resolved from other protein kinase activities by ion exchange chromatography. 5. Phosphatidylserine and Ca2+ were required for protein kinase C to be active. 6. Diacylglycerol and phorbol ester enhanced the activation of the enzyme.